Hybrid drive systems proposed in related art are configured such that an automatic transmission device is disposed on a first shaft that is coaxial with an engine output shaft, and an electric motor is disposed on a second shaft different from the first shaft, wherein a rotation is transmitted from an output shaft of the electric motor through a reduction gear to an input shaft of the automatic transmission device on the first shaft (see Patent Documents 1 and 2).
In the hybrid drive system described in Patent Document 1, the input shaft on the first shaft is supported by a case through a bearing, and a drive gear (first gear) to which power from the electric motor is transmitted is in spline engagement with and supported by the input shaft inside the case. Further, a portion of the input shaft projects outside the case and is connected to the engine output shaft through a clutch and a damper.
In the hybrid drive system described in Patent Document 2, a first gear disposed on the first shaft constitutes the gear that reduces the speed of the rotation from the electric motor, and a clutch that allows and cuts off power transmission between the engine output shaft and the input shaft of the automatic transmission device is disposed inside the first gear. The first gear is formed from a hollow structure that houses the clutch. An engine side of the first gear is supported by a partition (first support wall) through a first bearing, and a transmission device side of the first gear is supported by a pump body (second support wall) through a second bearing, such that the first gear has a structure supported on both sides. An intermediate shaft acting as an input side of the clutch is connected to the engine output shaft through the damper, and an output side of the clutch is connected to the first gear and the input shaft of the transmission device. The intermediate shaft is rotatably supported by the first gear through a needle bearing.